<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <title>练习</title>
    <!-- 不要忘记引入index.css -->
    <link rel="stylesheet" href="index.css">
</head>

<body>
    <div class=box>
        <input type="text" class="input">
        <div><span></span></div>
    </div>
   

</body>

</html>